Selective signaling circuits



Nov. 3, 1925.

M. R. GOWING SELECTIVE SIGNALING CIRCUITS Filed July 9, 1921 hue/varfi/fwxr/ce A 601W;

m 6mm E \SWES wawm 2 Patented Nov. 3, 1925.

UNITED STATES issases PATENT err-ice.

MAURICE R. GOWING, OF MOUNTAIN LAKES, NEW JERSEY, ASSIGNQR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., QORPQRATION OF YO BK.

SELECTIVE FSIGNALING CIRCUITS.

" Application filed July 9, 1921. Serial No. 483,432.

To all whom it mayconccrn."

Be it known that I, MAUnIcn R. GOWING, a citizen of the United States, residing, at Mountain Lakes, in the county of Morris, State of New Jersey, have invented certain new and useful Improvements in Selective Signaling Circuits, of which the'following is a full, clear, concise, and exact description. V

This invention relates to selective signaling circuits and more particularly to selective circuits for associating the sending and receiving branches of a tw0-way alternating current signaling system with a common transmission medium or line. The object of the invention is to provide a simple and effective arrangement or selective circuits for such a system. 1

In its preferred form, the invention is embodied in a carrier wave telephone system in which a plurality of two-way conversations may be carried on over a common transmission line. Distinctive frequencies are used for transmissions in oppo-' site directions and also for different transmissions in the same direction. Band-pass filters having series and shunt impedance elements are used in the sending and receiving circuits to allow the passage of current of desired frequencies to the respective circuits. the filters, both sending and receiving, are connected in series with each other and with the common transmission line.

This embodiment of the invention is shown in the drawing in which Fig. 1 is a multiplex terminal of a carrier wave telephone system and Fig. 2 a modification thereof.

Refering now to Fig. 1, multiplex carrier terminal station C and an ordinary telephone line L are connected to a common transmission line ML by means of a carrier composite set comprising a hi h-pass filter HPF and a low-pass filter LPF: The carrier terminal as shown comprises two twoway channels I and II. These channels have transmitting branches TB and T13 respectively, and receiving branches BB and BB respectively.

The shunt sections of all of An ordinary telephone line L connects an ordinary subscribers telephone station or a telephone exchange A to channel. I. The line L is conjugately connected to the transmitting branch TB and the receiving branch BB by means of the conjugate transformer or hybrid coil 5. The balancing network N connected to coil 5, balances the line L In the transmitting branch TB is an oscillation generator 0 a modulator M and a modulator band filter MBF The receiving branch BB comprises a detector band filter DBF a demodulator D a demodulator amplifier DA and a low pass filter LPF Y The oscillator 0 modulator M demodulator D and demodulator amplifier DA may be of any suitable design, but are preferably of the vacuum tube type. Devices suitable for this purpose are described, by E. H. Colpitts and O. B. Blackwell, in a paper entitled Carrier currenttelephony and telegraphyl published in the Journal of the American Institute of Electrical Engineers for April, May and June, 1921. The modulator band filter MBF and demodulator band filter DBF comprise series and shunt impedance elements and are preferably of the general type disclosed 'in Camp bell Patent No. 1,227,113 of May 22, 1917.

A subscribers station or ordinary telephone exchange 3B is connected to channel II by meansof an ordinary telephone line L Channel II is similar to channel. I ex,- cept that the constantsot the filters used therein'are such as t0 take care of the frequencies individualthereto.

The shunt impedance elements 6, 7, 8 and 9 of the several band filters are all connected in series with each other and with the primary of transformer 10 to make up a common terminal circuit. By means of transformer 0, this common terminal circuit is inductively connected through the high-pass filter IIPF to the common line ML.

At the distant end of the comm-on line ML is located another carrierterminal station adapted to cooperate with the terminal station shown. For each transmitting branch of the station shown, there is a c0- operating receiving branch at the distant station and for each receiving branch of the station shown, there is a cooperating transmitting branch at the distant station.

Distinctive frequencies are used for transmissions in opposite directions and for different transmissions in the same direction. Thus, each of the band filters MBF DEF, MBF and DEF are adapted to pass a distinctive band of frequencies, which f 'equeir cies are used for the transmission, characteristic of that branch.

In Fig. 1, two channels only of a multiplex system are shown, but it is to be understood that a greater or less number may be used. Regardless of the number of channels in the system, the end sections of all the band filters would be connected in series with each other and with the common line through a transformer such as transformer 10.

In an actual system which has been manuf'actured, carrier frequencies of 6, 9 and 12 kilocycles are used for transmission in one direction and frequencies of 15, 18 and 21 kilocycles for transmission in the opposite direction. In this system, the lower side bands of frequencies are used with the lower carrier frequencies and the upper side bands, with the higher frequencies. Also in this system, both the carrier frequency itself and the side band corresponding to the telephone message are transmitted from the sending station to the receiving station over the common line.

In the modification of Fig. 2, the common terminal circuit, comprising the shunt impedance elements 6, 7 8 and 9 connected in series with each other, is conductively connected to the common line ML. In other words, the transformer 10 has been omitted. In this modification, it is to be noted, the band filters in the transn'iitting branches are directly connected together and likewise those in the receiving branches, as distinguished from the staggered arrangement of Fig. l. lV-he'ther or not it is desirable to use either or both of the modifications of Fig. 2 will depend upon the physical, electrical and economical conditions of each installation.

lVhile the invention has been described in its embodiment in a carrier wave telephone system, it may well be, embodied in other systems where selective circuits are required. The scope of the invention is defined by the accompanying claims.

hat is claimed is:

1. In a carrier signaling system, a terminal station, a transmitting branch at said station, a receivingbranch also at said station, a band filter in each of said branches, each of said filters having a shunt impedance element, a common transmission medium, and means to connect a shunt impedance element of a filter in said transmitting branch and a shunt impedance element of a filter in said receiving branch in series with each other and with the common transmission medium.

2. in a carrier wave signaling system, a common transmission line, a carrier terminal station, a transmitting branch and a receiving branch at said station, a source of speech modulated carrier waves a band filter having shunt impedance elements for said transmitting branch, a demodulator for speech modulated carrier waves, another band filter having shunt impedance elements for the receiving branch, ineans to connect a shunt element of a transmitting bandffilter and a shunt element of a receiving band filter in series with each other, and means to associate the carrier terminal with the common line. I

3. In a multiplex signaling system, a terminal station, a transmission line, a plurality of transmitting branches at said terminal station, plurality of receiving branches also at said terminal station, a band filter in each of said branches, each of said filters having a shunt impedance element at one end thereof, means to connect all said end shunt impedance elements in series with each other, and means to associate said terminal station with said line.

4;. In a multiplex signaling systei'n, terminal station, a. transmission line, a collecting circuit coupled to said transmission line at said terminal. station, a plurality of transmitting branches and a pluralityof receiving branches at said terminal station, and a band filter in each f said transmitting and receiving branches having a shunt impedance element connected to said collecting circuit. I

5. In a multiplex signaling system, a terminal station, a transmission line, a collecting circuit at said terminal station, a transformer having its primary winding connect ed to said collecting circuit andi'ts secondary winding connected to said transmission line to enable two-way transmission between said circuit and said line, a plurality of tra nsmitting branches and a plurality of receiving branches at said terminal station, and aband filter in each of said branches having a shunt impedance element connected to said collecting circuit.

6. In a multiplex signaling system, a terminal station, a transmission line, a. plurality of transmitting branches and a plurality of receiving branches at said station, a source of speech modulated carrier waves associated with each of said transmitting branches, at demodulator, for speech modulated waves associated with each of said receiving branches, aband filter having series and shunt impedance elements in each of said transmitting and receiving branches to separate the respective bands of frequencies allotted thereto, there being a greater frequency separation between oppositely directed frequencies than between the frequencies transmitted in the same direction,

and means to connect a shunt impedance element of each of the band filters in both said transmitting and receiving branches in series with each other and with said trans- 1 mission line.

In witness whereof, I hereunto subscribe my name this 5th day of July, A. D. 1921.

MAURICE R. GOWING. 

